Chapter 3 - Thermal Physics

Question 1

What direction does thermal energy naturally flow in?

Answer 1

Flows from hot to cold.
The temperature difference between two objects in thermal contact will determine the direction of the thermal energy transfer.

Question 2

What is thermal equilibrium?

Answer 2

When two objects are placed in thermal contact they are expected to reach the same temperature.

Question 3

How to convert between Kelvins and Celsius, and what zero Kelvin means

Answer 3

T (K) = t (Celsius) + 273

Zero Kelvin is absolute zero where particles have no energy left. However this is impossible in reality because the particles would have to be in a vacuum.

Question 4

What is pressure in terms of gases, the equation and the units.

Answer 4

Pressure is the force per unit area from the gas acting 90 degrees on the container wall.
p = F/A
A = surface area
Units: Nm^-2 or Pa

Question 5

How to investigate how quantities are interrelated.

Answer 5

One quantity to be the independent variable, one to be the dependant and another to be the control

Question 6

Macroscopic point of view

Answer 6

Considers the system as a whole and how it interacts with the surroundings.

Question 7

Microscopic point of view

Answer 7

Looks inside the system on how the components interact with each other.

Question 8

How the particles act in terms of the kinetic theory and kinetic energy.

Answer 8

The particles are constantly in random motion and therefore have kinetic energy.
They can have translational kinetic energy ( whole molecule moving in a direction) or rotational kinetic energy (molecule is rotating about one or more axis)

Question 9

Why do particles have potential energy?

Answer 9

Because of the intermolecular energy between the particles.

Question 10

What is internal energy?

Answer 10

The total energy the particles have and when a substance is heated we increase its internal energy.

Question 11

Characteristics of a solid.

Answer 11

Fixed volume and shape, held in position by bonds.

The molecules vibrate around a mean position. The higher the temperature the greater the vibrations.

Question 12

Characteristics of a liquid.

Answer 12

Fixed volume but can change shape.
The molecules vibrate but not completely fixed in position
Still Strong forces between molecules

Question 13

Characteristics of a gas.

Answer 13

They will always expand to fill the container
Forces between molecules are weak and they are essentially independent of one another
Occasionally collide

Question 14

Connection between heat and work

Answer 14

Work is done on a microscopic level - we say heating is taking place. The energy transferred from the heat can increase the K.E or/ and the Potential energy of the particles.

Question 15

What three things does increases the temperature depend on?

Answer 15

Energy given to the object
The mass
The substance it’s made from

Question 16

What is Thermal capacity?

Answer 16

The energy required to raise its temperature by 1K

Question 17

What is Specific heat capacity

Answer 17

The energy required to raise a unit mass of a substance by 1K

Question 18

What happens when an object is raised above room temperature.

Answer 18

It starts to lose energy until the surrounding temperature is the same as the objects. The hotter it becomes the greater the rate at which loses energy.

Question 19

Equation for the specific heat capacity in an circuit.

Answer 19

c = (Ix t x V) / m ( T2 - T1)

Question 20

What occurs when there are two different mixtures at different temperatures?

Answer 20

Energy lost by hot substance cooling down = energy gained by cold substance heating up

Ma x Ca (Ta - Tmax) = Mb x Cb (Tmax - Tb)

Question 21

What is the universal constant and what is the equation for it?

Answer 21

Universal constant = molar gas constant = R
Units for R: J mol^-1 K^-1

pV/ nT = R

Question 22

What is an ideal gas?

Answer 22

A gas that follows the gas laws for all the values of p, V, and T
Thus is cannot be liquefied.

Question 23

What is molar mass and what’s its equation?

Answer 23

It’s the mass of one mole of a substance

No. of moles = number of atoms/ Avogadro constant

Question 24

When can real gases approximate to ideal behaviour?

Answer 24

The intermolecular forces are small enough to ignore, therefore the pressure/ density of the gas must be low with moderate temperature.

Question 25

What is Boltzmann’s constant and the equation for it?

Answer 25

It’s a constant ( the actual value is in the booklet)

It’s the idea that absolute temperature is proportional to kinetic energy of a gas molecule.

Question 26

What are the assumptions of the kinetic model of an ideal gas?

Answer 26

1). Newton’s laws apply to the molecules.
In collisions:
It’s the only time there are intermolecular forces
They are elastic
No time spent

Molecules are treated like points and are in random motion.

Question 27

What happens to a molecules momentum once it bounces off a wall?

Answer 27

It changes due to the change in direction (momentum is a vector)

Question 28

What effect does the pressure of molecules hitting the wall have, in a microscopic point of view?

Answer 28

The average of all the microscopic forces on the wall over a period of time means there’s a constant force on the wall.

Question 29

What’s the pressure law?

Answer 29

At a constant volume, the pressure of a gas is proportional to the temperature.

More kinetic energy means a greater change in momentum when they hit the wall, thus a bigger force.

Question 30

What is Charles’s law?

Answer 30

At a constant pressure, the volume of a gas is proportional to its temperature in Kelvins.

If the volume of a gas increases, the rate of collisions must go down so the average force on the wall (pressure) remains constant.

Question 31

What is Boyle’s Law?

Answer 31

At a constant temperature, the pressure of a gas is inversely proportional to its volume.

Constant temperature means constant kinetic energy (speed) of the molecules.
Increase the volume will decrease the pressure
Decrease the volume will increase the pressure

Question 32

What happens to the temperature when a substance changes phase, and therefore the energy?

Answer 32

It remains constant even though thermal energy is still being transferred. Thus kinetic energy doesn’t increase, so the potential energy increases instead, as bonds are being broken which takes energy, or bonds are being made which releases energy.

Question 33

What is latent heat?

Answer 33

It’s the amount of energy associated with the phase change

Question 34

What’s it called when a solid changes to a liquid?

Answer 34

Fusion

Question 35

What’s it called when a liquid changes into a gas?

Answer 35

Vaporisation

Question 36

What is specific latent heat and its unit?

Answer 36

The amount of energy per unit mass absorbed or released during a change of phase
Unit: J kg^-1

Question 37

What would happen in an ideal situation of no energy loss?

Answer 37

A constant rate of energy transfer thus a constant rate of increase of temperature until the point of a phase change.

Question 38

What’s the difference between the specific heat capacity of a liquid than a solid?

Answer 38

The specific heat capacity of a liquid is less than a solid. A given amount of energy will cause a greater increase in the temperature for the liquid than the solid.

Question 39

An experiment and equation of measuring the specific heat capacity of fusion of water

Answer 39

Ice is added to warm water and the temperature of the mix is measure.
If no energy is lost from the system:
Energy lost by the water cooling down = the energy gained by the ice
M(w) x c(w) (Tw - Tmix) = M(ice) x L(fusion) + M(i) x c(w) x T(mix)